Chromosome
hideA chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes. Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000 nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.
In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.
However, in practice "chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.
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News tagged with chromosomes
Genome sequence for the domestic horse unveiled
Nov 05, 2009 |
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The whole genome sequence of the domestic horse has been completed by the genome-sequencing center of The Broad Institute of MIT and Harvard, in collaboration with an international team of researchers that ...
Singapore scientists describe novel method for 3-D whole genome mapping research
Nov 04, 2009 |
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In this week's Nature, Genome Institute of Singapore (GIS) scientists report a technological advance in the study of gene expression and regulation in the genome's three-dimensional folding and looping state through the de ...
Drought tolerant cowpea can improve crop yield in arid West Africa
Nov 03, 2009 |
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Even the highly drought-resistant cowpea (a long type of legume) now has an increasingly difficult time surviving in the Sahel countries where climate change has resulted in shorter and less frequent rainy seasons. Wageningen ...
Cucumber genome published
Nov 02, 2009 |
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The genome of the cucumber has been sequenced by an international consortium lead by Chinese and U.S. institutions. The annotated genome is published online Nov. 1 by the journal Nature Genetics.
New insights into Australia's unique platypus
Nov 02, 2009 |
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(PhysOrg.com) -- New insights into the biology of the platypus and echidna have been published, providing a collection of unique research data about the world's only monotremes.
Researchers discover mechanism that prevents two species from reproducing
Oct 26, 2009 |
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Cornell researchers have discovered a genetic mechanism in fruit flies that prevents two closely related species from reproducing, a finding that offers clues to how species evolve.
Rare mutation dramatically increasing schizophrenia risk
Oct 25, 2009 |
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An international team of researchers led by geneticist Jonathan Sebat, Ph.D., of Cold Spring Harbor Laboratory (CSHL), has identified a mutation on human chromosome 16 that substantially increases risk for schizophrenia.
Mice regain ability to extend telomeres suggesting potential for dyskeratosis congenita therapy
Oct 19, 2009 |
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The human genetic disease dyskeratosis congenita (DKC) is an autosomal dominant disease that leads to abnormalities in tissues with a rapid cell turnover - the skin, nails, bone marrow, lungs and gut. Patients with DKC experience ...
New cancer gene discovered
Oct 13, 2009 |
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A new cancer gene has been discovered by a research group at the Sahlgrenska Academy at the University of Gothenburg, Sweden. The gene causes an insidious form of glandular cancer usually in the head and neck and in women ...
Genes behind increasingly common form of cancer identified
Oct 13, 2009 |
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Researchers at the University of Gothenburg, Sweden, have identified two genes believed to play a role in the development of endometrial cancer. These results may eventually lead to better diagnosis and treatment of this ...
How does a worm build a throat? Tackling the 'organ formation puzzle'
Oct 06, 2009 |
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(PhysOrg.com) -- Mention worms to most people, and they probably think of fishing, gardening, or trips to the vet. Mention them to Susan E. Mango, and she begins telling you how “absolutely beautiful” they ...
Protein helps cells duplicate correctly, avoid becoming cancer
Oct 05, 2009 |
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A Purdue University researcher has discovered that the absence of certain proteins needed for proper cell duplication can lead to cancer.
US trio win Nobel Medicine Prize for research into ageing (Update 3)
Oct 05, 2009 |
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Australian-American researcher Elizabeth Blackburn and Carol Greider and Jack Szostak of the United States won the Nobel Medicine Prize on Monday for identifying a key switch in cellular ageing.
Genetic conflict in fish led to evolution of new sex chromosomes
Oct 01, 2009 |
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University of Maryland biologists have genetically mapped the sex chromosomes of several species of cichlid (pronounced "sick-lid") fish from Lake Malawi, East Africa, and identified a mechanism by which new ...
Researchers determine the composition of centromeric chromatin
Sep 28, 2009 |
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The Stowers Institute's Gerton Lab has provided new evidence to clarify the structure of nucleosomes containing Cse4, a centromere-specific histone protein required for proper kinetochore function, which plays a critical ...
